Well for one you dont add the R134 to the compressor, you add using the service ports.
Secondly lots of things can cause the compressor to go bad, reed valves inside will fail, the bearings on the pullies lock up.
One way to find problems using is an AC system is very easy an accurate and I know you have the tool, infact your using it right now. Your hands. Hot/warm/colc/cold. Line from the compressor to condensor should be hot, line from condensor to reciever/drier should be warm, line from receiver/drier to evaportor, cold, and evap. to compressor should be cool.
Theres your place to start, if you touch the line from the compressor to condensor and its cold, or cool, your compressor is shot to crap.
hope that helps
